Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
A New Sedimentary Model for the Qiangtang Basin, Tibet, China
(1) Chengdu Institute of Geology and Mineral Resources, Chengdu, China.
A paleoweathering-crust regolith from decimeters to a meter thick was discovered recently in the Qiangtang Basin, overlying diachronously upon the Upper Triassic (?) Xiaochaka Formation and its underlying strata including the Permian-Carboniferous. The regolith was then onlapped by the continental volcanic rocks, sedimentary-volcaniclastic rocks, and alluvial-fluvial sandstones and conglomerates from the Nadigangri Formation. Obviously the Nadigangri Formation represents the onset of a new sedimentary succession in the Qiangtang Basin. The SHRIMP zircon U-Pb isotopic dating gives the ages of 219.5 ± 2.1 Ma and 219 ± 2 Ma for the basalt and granodiorite from central Qiangtang, and 216.8 ± 2.1 Ma and 217.3 ± 2.5 Ma for the vitric tuff and crystal tuff from the Shenglihe and Wanghuling regions in the central and northern Qiangtang Basin. All these age determinations imply that the Nadigangri Formation volcanic rocks, and then the onset of the Mesozoic Qiangtang Basin should be of Late Triassic rather than just early or middle Jurassic as reported previously. The deposition had displayed a transition from the continental to marine sedimentary environments during the early evolution of the Mesozoic (i.e. T3-K1) Qiangtang Basin. The sedimentary onlapping started from the alluvial-fluvial sedimentation, accompanied by magma intrusion, volcanic eruption and pyroclastic deposition. This was followed by a basinwide rapid subsidence and a development of marine-dominated succession including carbonates over 1200 meters thick. The new basin model implied a different evolution of hydrocarbon systems in the basin.